• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.7
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• pp.992-1000
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• 1998

In the present study the behavior of laminar-wavy film flowing down a vertical plate was studied analytically. The effects of film Reynolds number and interfacial shear stress on the mean film thickness, wave amplitude, wave length, and wave celerity were analysed. The anayltical results on the periodic-wave falling film showed good agreements with experimental data for Re < 100. As the film Reynolds number increased, mean film thickness, wave amplitude, and wave celerity increased, but wave length decreased. Depending on the direction of interfacial shear stress, the shape of wavy interface was disturbed significantly, especially for the intermediate-wave. As the interfacial shear stress increased, for the periodic-wave film, wave amplitude and wave celerity increased, but mean film thickness and wave length decreased.

• Steel and Composite Structures
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• v.8 no.6
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• pp.457-473
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• 2008

Yielding of the internal steel reinforcement is an important mechanism that influences the Intermediate Crack-induced debonding (IC debonding) behavior in FRP-strengthened RC members since the FRP is required to carry additional forces beyond the condition of steel yielding. However, rational design practice dictates an appropriate limit state is defined when steel yielding is assured prior to FRP debonding. This paper proposes a criterion which correlates the occurrence of IC debonding to the formulation of a critical steel yielding length. Once this length is exceeded the average bond stress in the FRP/concrete interface exceeds its threshold value, which proves to correlate with the average bond resistance in an FRP/concrete joint under simple shear loading. This proposed IC debonding concept is based on traditional sections analysis which is conventionally applied in design practice. Hence complex bond stress-slip analyses are avoided. Furthermore, the proposed model incorporates not only the bond properties of FRP/concrete interface but also the beam geometry, and properties of steel and FRP reinforcement in the analysis of IC debonding strength. Based upon a solid database, the validity of the proposed simple IC debonding criterion is demonstrated.

• Transactions of Materials Processing
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• v.15 no.2 s.83
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• pp.132-137
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• 2006

This paper is concerned with the thermo-mechanical behavior including temperature dependent strain-rate sensitivity of steel sheet for an auto-body. In order to identify the temperature dependent strain-rate sensitivity of SPRC35R and SPRC45E, uniaxial tension tests are performed with the variation of the strain-rates from 0.001 /sec to 200 /sec at environmental temperatures varied from $-40^{\circ}C\;to\;200^{\circ}C$. The thermo-mechanical response at the quasi-static state is obtained with the static tensile test and at the intermediate strain-rate is from the high speed tensile test. Experimental results show that the strain-rate sensitivity increases at low temperature. It represents that as the strain-rate increases, the variation of flow stress becomes sensitive on the temperature. The results indicate that the flow stress of SPRC35R is more dependent on the changes of strain-rate and temperature than those of SPRC45E.

• Korean Journal of Materials Research
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• v.23 no.10
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• pp.568-573
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• 2013

The deformation properties of a TiC-Mo eutectic composite were investigated in a compression test at temperatures ranging from room temperature to 2053 K and at strain rates ranging from $3.9{\times}10^{-5}s^{-1}$ to $4.9{\times}10^{-3}s^{-1}$. It was found that this material shows excellent high-temperature strength as well as appreciable room-temperature toughness, suggesting that the material is a good candidate for high-temperature application as a structure material. At a low-temperature, high strength is observed. The deformation behavior is different among the three temperature ranges tested here, i.e., low, intermediate and high. At an intermediate temperature, no yield drop occurs, and from the beginning the work hardening level is high. At a high temperature, a yield drop occurs again, after which deformation proceeds with nearly constant stress. The temperature- and yield-stress-dependence of the strain is the strongest in this case among the three temperature ranges. The observed high-temperature deformation behavior suggests that the excellent high-temperature strength is due to the constraining of the deformation in the Mo phase by the thin TiC components, which is considerably stronger than bulk TiC. It is also concluded that the appreciable room-temperature toughness is ascribed to the frequent branching of crack paths as well as to the plastic deformation of the Mo phase.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.2 s.257
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• pp.174-181
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• 2007

This paper is concerned with the thermo-mechanical behavior of steel sheet for an auto-body including temperature dependent strain rate sensitivity. In order to identify the temperature-dependent strain rate sensitivity of SPRC35R, SPRC45E and TRIP60, uniaxial tensile tests are performed with the variation of the strain rates from 0.001/sec to 200/sec and the variation of environmental temperatures from $-40^{\circ}C$ to $200^{\circ}C$. The thermo-mechanical response at the quasi-static state is obtained from the static tensile test and that at the intermediate strain rate is obtained from the high speed tensile test. Experimental results show that the variation of the flow stress and fracture elongation becomes sensitive to the temperature as the strain rate increases. It is observed that the dynamic strain aging occurs with TRIP60 at the temperature above $150^{\circ}C$. Results also indicate that the flow stress and tincture elongation of SPRC35R are more dependent on the changes of strain rates and temperature than those of SPRC45E and TRIP60.

• Journal of Surface Science and Engineering
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• v.30 no.4
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• pp.272-280
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• 1997

The Thermal Barrier Coation(TBC) to improve the that barrier and wear resistant propenrty in high temperature ofthe aircraftength between the accumlation of the aircraft engine and the automobile engine has usually the two layer structure. One is a creamic top layer for heat insulation and the other is a metal bond layer to facilitate the bond strength between the top ceramic layer and the substrate. But, the coated layers should be peeled off because of the accumulation of the thermal stress by the differance of the thermal expantion coefficient between metal and ceramics in a hrat cyclic environment. In this study, the intermediate layer by plasm spray process was introduced to reduce the thermal stress. The powders of plasm spray coating were the Yttria Stabilized Zirconia (YSZ), the Magnesia Stabillized Zirconia(MSZ) and NiCrAlY. the intermediate layer was sprayed with the powders of the bond cast for the purpose of test were executed. The high temperature wear resistance tends to decreasnceee wear and thermal shock test were exeucuted. The high temperature were resistance of the YSZ TBC is better that of the MSZ TBC. The wearrsistance tends to decrease accoring to incresing the temperature between $400^{\circ}C$to $600^{\circ}C$. The thermal shock life of the 3 layer TBC with YSZ top casting was the most outstanding thermal shock rsisstasnce. This means that the intermediate layer should play an importnat roll to alleviate the diffrerence of the thermal expansion coef frcients between metallic layer and cermics layer.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.231-239
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• 2003

Many box girder bridges have been constructed during the past several decades due to their large bending and torsional rigidities as well as aesthetic considerations. However, box girders have shortcoming in that the cross section distorts under an eccentric loading and warps out of the section plane. Therefore, in order to reduce distortional stresses such as distortional warping and transverse bending normal stresses, diaphragms were generally installed in the box girders. Shapes of the diaphragms in steel-box-girder bridges constructed up to date were solid-plate, frame, and truss types. The objectives of this study using parametric study were to evaluate the appropriate stiffness ratio of intermediate diaphragms and then to propose the effective spacing and numbers of intermediate diaphragms based on the evaluated stiffness ratio. Target bridges for this study were straight continuous span bridges with a single-cell steel box section. The parameters for the parametric study were the shape of box section, the span numbers, the equivalent span length, the stiffness of intermediate diaphragms, and the spacing of intermediate diaphragms. From the results of the parametric study, the effective spacing and numbers as well as the stiffness ratio of the intermediate diaphragms will be presented.

• The Journal of the Convergence on Culture Technology
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• v.8 no.3
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• pp.551-557
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• 2022

Geotechnical risk factors encountered in intermediate-depth underground tunnel construction are diverse, and the types and standards of risk factors are different according to the depth and regional geological characteristics of Korea. In order to understand the effects of geological characteristics and geologic structure on safety, which show various porous characteristics of urban underground complex ground, the risk factors of intermediate-depth rock mass in Korea were analyzed based on domestic and foreign cases. As a result of the study, seven categories affecting the stability of the intermediate-depth tunneling, namely, geologic structure, rock characteristics, hydrogeology, overburden, high stress, ground characteristics and artificial structures, and about 22 risk factors were derived. We present the risk criteria and interval values for risk evaluation of faults, folds, dikes, and rocks that have the greatest influence among risk factors. Criteria and interval values for other risk factors are under study.

• Korean Journal of Ecology and Environment
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• v.45 no.3
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• pp.314-321
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• 2012

To quantitatively assess the effects of turbidity on egg development and larval fish survival, a laboratory fish rearing experiment was applied to different life stages (newly hatched larval stage, juvenile stage and pre-adult stage) of the Zacco platypus, one of the most universal and tolerant species in Korea. According to the stress index of turbidity in water with exposure time, three different treatments, including a reference condition (1~7 NTU) as well as intermediate (20~150 NTU) and high turbidity conditions (400~1,000 NTU) were applied, and egg hatching and larval fish mortality rates were observed. The mortality rates of newly hatched larval fish were significantly different among treatments (ANOVA, $F_{2,3}$=17.79, p<0.05). Average rates of survival to hatching were 20.9% (${\pm}0.1%$) for reference condition, 11% (${\pm}6.9%$) for intermediate level and 3.2% (${\pm}3.7%$) for high level conditions, respectively. A sudden change of mortality at the high level was observed within 5 days of the experiment. About 84% of juvenile fish survived until 20 experimental periods under conditions of reference turbidity, while survival under conditions of intermediate turbidity was over 80% of larval fish until day 13 of the experiment, but dropped to less than 10% after day 14 and 15 of two experiments. Fish mortality appeared from day 6 of the high turbidity experiment, and 50% mortality was achieved at day 9 to 10 of experiment. Full mortality occurred at day 14 of the experiment (RM-ANOVA, $F_{2,38}$, p<0.005). In the pre-adult stage experiment, no mortality was observed during the experiment at reference level treatment (20 days), while only slight mortality rates were observed for both intermediate and high levels until day 5 of the experiment, however, no further fish died in either experiment. It was significantly different compared to reference condition (RM-ANOVA, $F_{2,20}$=8.28, p<0.01), but no difference was observed between intermediate and high level conditions. Consequently, this tolerant species has been determined to be well adapted to high levels of turbidity in its adult stage, but more vulnerable throughout earlier life stages.

• Journal of Digital Convergence
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• v.11 no.9
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• pp.279-287
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• 2013

This study has attempted to investigate the effect of the stress of college life and self-efficacy on depression against 366 students from beauty-related colleges. First, according to analysis on the stress of college life, self-efficacy and depression levels, the stress of college life was an intermediate level or lower (M=2.40). Among subordinate factors, 'academic performance' was the highest, followed by 'future career' and 'economic difficulties' in terms of a stress level. The self-efficacy was more than an intermediate level (M=3.21). Among subordinate factors, 'self-regulation' was the highest while 'difficult assignment' was the lowest in terms of a stress level. Second, the stress of college life showed a negative correlation with self-efficacy but positive correlation with depression. In addition, a negative correlation was observed between self-efficacy and depression. Third, in the stress of college life, 'academic performance' and 'values' had a positive effect. In self-efficacy, 'academic performance' and 'values' revealed a positive effect while 'confidence' and 'self-regulation' had a negative effect on depression.